1. Field of the Invention
This invention relates to a view point detecting apparatus suitable for use in a video camera, a still camera or the like.
2. Related Background Art
Various ideas of using the photographer's visual axis (so-called automatic pursuit using the visual axis) to determine an area for controlling the operations of a camera have heretofore been proposed, and for example, in Japanese Laid-Open Patent Application No. 63-94232, a description has been provided as follows.
FIG. 8 of the accompanying drawings shows a block diagram of a construction according to the prior art.
In this example of the prior art, the movement of the eyeball of the photographer observing a photographed image through a finder or a monitor device is monitored and the automatic focusing operation and the automatic exposure operation are performed in an area including that portion of the image field which is gazed at by the photographer. The reference numeral 30 designates a detector of eye movement. This detector 30, the details of which will be described later, detects the movement of the photographer's eyeball 32, and sends to a gate control circuit 34 a position signal (horizontal position and vertical position) indicative of which position in the image field the eye is looking at. The gate control circuit 34 compares a horizontal synchronizing signal Hsync and a vertical synchronizing signal Vsyn from a clock circuit 28 with the position signal from the detector of eye movement 30, controls a gate circuit 14 and passes therethrough only the image signal of a corresponding area on the image field.
There are various principles of detecting eye movement, and herein the system of Nippon Hoso Kyokai (NHK) will be described as an example (see Television Society journal vol. No. 2 (1986), p. 41 and so on). The optical system portion of the NHK's system is shown in FIG. 9 of the accompanying drawings, and a specific circuit when it is applied to the detector of eye movement 30 in the embodiment of FIG. 8 is shown in FIG. 10 of the accompanying drawings with the gate control circuit 34. As shown in FIG. 9, infrared light is applied from an infrared light source 40 (40X, 40Y) disposed in proximity to the eyeball, and the reflected light therefrom is received by photoelectric conversion elements 42 (42R, 42L; 42U, 42D) and the rightward and leftward movement and upward and downward movement of the iris are detected. The photoelectric conversion elements 42R and 42L for detecting the rightward and leftward movement of the iris are disposed so as to receive the reflected lights from the right side and the left side, respectively, of the iris in a front-facing state, and the outputs thereof are subtraction-amplified by a subtract amplifier 44. Also, the photoelectric conversion elements 42U and 42D for detecting the upward and downward movement of the iris are both disposed so as to receive the reflected light from the obliquely lower position of the iris in a front-facing state, and the outputs thereof are addition-amplified by an add amplifier 46.
The output of the subtract amplifier 44 exhibits the characteristic as shown in FIG. 11A of the accompanying drawings to the rightward and leftward movement of the iris, and the output of the add amplifier 46 exhibits the characteristic as shown in FIG. 11B of the accompanying drawings to the upward and downward movement of the iris. After all, the output of the subtract amplifier 44 indicates the direction of the iris in the horizontal plane (speaking in terms of the observation image field being observed by the observer, the horizontal position thereof), and the output of the add amplifier 46 indicates the direction in which the iris faces in the vertical plane (speaking in terms of the observation image field, the vertical position thereof). Actually, however, the outputs of the subtract amplifier 44 and the add amplifier 46 exhibit more or less non-linearity and therefore, it is preferable to provide linearity compensation circuits 48 and 50 in order to enhance detection accuracy.
Accordingly, in FIG. 10, the output of a compensation circuit 48 indicates a horizontal position x in the image field image and the output of a compensation circuit 50 indicates a vertical position y in the image field image.
Also, the assignee has proposed apparatuses for detecting the visual axis in U.S. Pat. No. 5,036,347, U.S. applications Ser. Nos. 406,588 (filed on Sep. 13, 1989), and 746,462 (filed on Aug. 16 1991), U.S. Continuation applications Nos. 671,656 (filed on Mar. 19, 1991) and 807,621 (filed on Dec. 13, 1991).
However, in the above-described examples of the prior art, even if the photographer's visual axis can be detected, the visual axis is detected as having likewise shifted when the photographer momentarily looks, for example, at the outside of the frame of the required photographing image field and the change-over or the like of the AF area based on the visual axis is effected and therefor, the reverse effect of using visual axis detection is provided.